1. Field of the Invention
It relates to a method of balancing a yarn winder, more particularly, to a method of balancing a yarn winder which enables a stable take-up of synthetic filament yarn spun from a spinning apparatus at a high speed while avoiding serious spindle vibration.
2. Description of the Related Art
Recently, an increase in the speed of a synthetic fiber manufacturing process has been made to improve the productivity of the process and the quality of a yarn thus produced. Particularly, in a novel process, a full oriented yarn [FOY] having good mechanical properties durable in practical use is obtained directly from a spinning apparatus by continuously connecting the spinning and drawing processes, in which the yarn is taken up at a rate in a range of from 5,000 m/min to 6,000 m/min. This means that a high speed take-up winder is now in practical use.
Along with the increased speed of the winder, a winder provided with a longer spindle compared to a standard spindle having a total length of, for example, 600 mm for carrying four bobbins having a length of 150 mm, or 1,200 mm for carrying eight bobbins, is desirable in order to improve the productivity and to decrease the cost of production of the yarn. Moreover, there is also a strong need to minimize the number of operators necessary for the threading operation and decrease the amount of waste accompanying this operation.
Under these circumstances, it has become very important to develop a method of balancing a yarn winder provided with a long spindle rotatable at a high speed while carrying a multiple of bobbins thereon, particularly with an automatic yarn transfer device.
In considering the vibrations encountered in a spindle the term "critical speed of a spindle" is a generic term encompassing all of the first, second and third critical speeds all of which produce violent lateral vibrations of the spindle as its speed of rotation increases above zero. Specific critical speeds are defined as follows:
The first critical speed, sometimes called the primary critical speed, is the critical speed of the spindle which first occurs as the speed of rotation is increased from zero. The second critical speed is the critical speed of rotation of the spindle which occurs secondly as the speed of rotation is increased above the first critical speed. It arises mainly from the vibration of the tubular supporting member.
The third critical speed of the spindle is another of the critical speeds of the spindle and is the third to occur as the speed of rotation is further increased above the second critical speed. It arises mainly from the vibration of the rearward cylindrical hollow body of the bobbin holding portion of the spindle.
One of the most serious problems arising when a winder with the long spindle is put into practice, is vibration of the spindle when rotating at a high speed. There are two ways to minimize the vibration; one is to increase the stiffness of the spindle and use the same in a rotational range beneath the first critical speed of the spindle which is one of the critical speeds of the spindle at each of which a violent lateral vibration of the spindle occurs, and which appears firstly during increasing of rotational speed of the spindle from zero, hereinafter referred to as the first critical speed. This, however, is almost impossible in practice, because it is very difficult to increase the stiffness of the spindle due to the longer size thereof. Accordingly, the other way is more frequently adopted, which is disclosed in, such as U.S. Pat. No. 3,917,182 granted to E. Lenk, Nov. 4, 1975, or Japanese Examined Patent Publication (Kokoku) No. 57-34187 of Mitsubishi Heavy Industries Co., Ltd., July 21, 1982, and utilizes a spindle having a flexible structure able to withstand a rotation above the first critical speed.
For example, to obtain a good yarn package by taking up a yarn on a bobbin having a length of 150 mm and a diameter of 110 mm mounted on a spindle, at a linear speed of 6,000 m/min, there must not be any critical speeds of the spindle, hereinafter referred to as the critical speed, in a wide working range of the spindle rotation of from 17,360 rpm at the starting stage to 4,550 rpm at the final stage of a full package.
Therefore, various factors affecting the stiffness of the spindle, such as a diameter of a shaft of the spindle, or a position of a bearing means rotatably supporting the shaft, should be determined to exclude the critical speed from the working range of the rotation of the spindle.
In practice, it is very difficult to take up a yarn in a stable condition only by excluding the critical speed from the working range, and generally, it is very difficult to machine a long spindle with a sufficient accuracy to eliminate bending of the shaft and eccentricity between the inner and outer diameters of the spindle, which results in a considerable unbalance in the spindle.
Accordingly, even though the respective parts, such as a shaft of a spindle or an element of a bobbin holding mechanism, are accurately balance-corrected with a balancing device in a low speed range, a complete elimination of unbalance is impossible and a satisfactory balance cannot be achieved.
Moreover, during assembly of the spindle and incorporation of the same into a winder, a new unbalance may be added due to discordance between the axes of a spindle and a mechanism for holding a bobbin on the spindle and the eccentricity of bearing means for mounting the spindle.
When the spindle is driven to rotate in such circumstances, a centrifugal force is generated in the first critical speed area due to the above unbalance, which causes a large vibration and noise at the winder. In such a case, the bearing means is subjected to an excessive force, which lowers the life of the bearing means, and in an extreme case, damages the spindle shaft. Also, this vibration degrades the quality of a yarn package formed on the spindle, and deteriorates the labour environment.
Accordingly, it is necessary to remove the residual unbalance from the completed spindle assembly by the balance-correcting operation, referred to as "field balancing".
The present inventors tried to correct a dynamic unbalance of a spindle for holding bobbins thereon, having a considerable residual unbalance therein due to its longer size, by field-balancing only in two correcting planes defined at the opposite extremities of the spindle. It was, however, impossible to remove the mass unbalance continuously distributed on the spindle along the length thereof only by correcting the dynamic unbalance in the planes of the opposite ends, and the vibration of the spindle was not decreased not only when passing the critical speed but also while normally winding a yarn at a working speed of the spindle. This is because the unbalance non-uniformly distributed in the spindle has a complicated influence on the first critical speed, and the respective vibration levels in the area of the working rotation cannot be corrected by a simple field-balancing in only the two end planes.
Further, it was found that if the vibration of the spindle is restricted to a lower level when the spindle speed passes the first critical speed, the vibration in a range of the working rotation of the spindle becomes larger, and vice versa, and thus the vibrations occurring when passing the first critical speed and in the working rotation area could not be simultaneously suppressed. In general, since the vibration in the working rotation area is limited to a lower level, the other vibration when the spindle passes the first critical speed must reach the higher level.
The spindle necessarily passes the first critical speed twice during the cycle of starting, acceleration, deceleration, and stop of the winder, whereby a bearing means for rotatably supporting the spindle suffers from an excessive force originated from the vibration and the lift thereof is lowered, which vibration is transmitted to a machine frame and may loosen screw connections in the machine, causing an unsafe condition therein.
The abovesaid drawbacks are particularly significant in a winder with an automatic yarn transfer device. In the winder of this kind, a yarn package is formed on a bobbin or bobbins mounted on a first spindle and pressed thereon at a predetermined pressure by means of a touch roll through the transverse reciprocation of a yarn by a traversing device, which package must be doffed from the first spindle when the same is full. Before the first spindle is stopped, a second spindle mounting fresh bobbins thereon is accelerated from a stationary state to a working speed, during which acceleration the second spindle must pass the first critical speed and the vibration thereof becomes very large. This vibration is transmitted to the first spindle, the touch roll, and a lifting box supporting the traversing device through the machine frame, and finally causes the lifting box to vibrate. Because of this disturbance, the yarn package being formed on the first spindle becomes unstable, causing deformation of the appearance and damage to the as-wound yarn by the periodic change of the pressure between the touch roll and the yarn package. In an extreme case, the yarn package jumps from the touch roll, whereby the yarn is released from the traversing device and a failure of the take-up operation occurs.
Further problems occur in the manufacture of a long spindle. In general, a bobbin carrying portion of such a long spindle is a single hollow cylinder, and a tubular member for holding the bearing means of a spindle shaft is projected from a machine frame and inserted into the interior of the hollow cylinder, as disclosed in the aforesaid U.S. Pat. No. 3,917,182 and Japanese Examined Patent Publication (Kokoku) No. 60-5508. To obtain such a spindle structure, a long hollow portion must be drilled in the spindle. In the case of a standard spindle, having a length of, for example, 600 mm, for mounting four bobbins thereon, the above boring may be carried out correctly. In the case of a longer spindle having a length exceeding, for example, 1,000 mm, length, however, it is very difficult to support the spindle without eccentricity during the boring of the long hollow portion. In addition, the drill bit must be supported at a tip end of a long and narrow shank having less rigidity, whereby the drill bit may be bent and deviated from the correct axis during the operation and provide an eccentric boring. Accordingly, a significant difference in a wall thickness may exist along the length of the spindle, which inevitably causes the vibration, and in an extreme condition, the spindle speed cannot exceed the first critical speed.
In addition, the eccentricity of bobbins relative to the spindle mounting the same also causes the above dynamic unbalance.